An organic electroluminescent device is a device which spontaneously emits light, and the principle of light emission thereof is as follows. When charges are injected into an organic layer between a hole injection electrode and an electron injection electrode, electrons and holes encounter, combined, and then annihilated, and thus light is generated. Organic electroluminescent devices have the characteristics of low voltage, high brightness, wide view angle, or the like. Therefore, organic electroluminescent devices have been rapidly developed in recent years. Among these, the white organic electroluminescent devices have become hot spots of investigation due to the wide prospect for application in terms of display, illumination, or the like.
Trivalent iridium complexes are considered as ideal organic electroluminescent materials in both the academic world and the industrial world all the time due to the advantages of high light-emitting effectiveness, adjustable color of light emission, or the like. A number of domestic and foreign research teams have intended to improve the overall properties of the white organic electroluminescent devices by starting with aspects of material synthesis and device optimization so as to meet the requirement for industrialization. For Example, in 2006, Forrest et al at Princeton University in United States designed a white organic electroluminescent device having a structure with multiple light-emitting layers, by doping a blue light material, a green light material and a red light material in different light-emitting layers respectively. Although that device exhibits relatively ideal white light emission, the device has relatively low efficiency and brightness and relatively high working voltage, due to unbalanced carrier injection. Additionally, complex structure of the device further results in relatively high manufacturing cost of the device
In order to solve these problems, in 2008, Kido et al at Yamagata University in Japan designed a structure of device having double light-emitting layers, to combine a blue-green light and an orange-red light, so as to obtain a white-light-emitting device successfully. That device has relatively high light-emitting effectiveness, but the feature of double-peak emission results in that the spectrum of the device does not have enough coverage degree in the white-light region, and thus the color restoration coefficient is relatively low. Further, as the brightness of the luminescence increases, the emission spectrum of the device varies greatly. As thus can be seen, the overall properties, such as light-emitting effectiveness, brightness, spectral stability, service life, and the like, of the white organic electroluminescent device are still not effectively improved.